The present invention relates to a vane-type rotary machine suitable for use as a compressor, pump or the like apparatus.
Vane-type rotary machines are well known and generally used as compressors, pumps or the like. The vane-type rotary machine is provided with a cam ring with an inner peripheral contour which is represented by an epitrochoid-like curve having n lobes (n being a natural number), and a rotatable cylindrical rotor housed by the cam ring and adapted to make contact with the cam ring at n points. The rotor is provided with a plurality of radial vane grooves which are communicated with one another at the bottoms thereof, and vanes slidably and reciprocatably received by respective vane grooves and adapted to be pressed at their outer ends to the inner peripheral surface of the cam ring.
As shown in FIG. 1, a cam ring 1 has an inner peripheral surface of a contour which is expressed by an epitrocoid-like curve having a plurality of lobes, three lobes in this case, with a cylindrical rotor 3, having a plurality of vane grooves 2, being disposed in the cam ring 1 in contact with the latter. Vane grooves 2 receive vanes 4 which are held in resilient contact with the inner peripheral surface of the cam ring 1. When this vane-type rotary machine operates as a compressor, vanes 4 reciprocatingly move in respective vane grooves 2 while making sliding contact with the inner peripheral surface of the cam ring 1 as the rotor 3 rotates. Consequently, the volumes of the spaces 5 defined by the vanes 4, rotor 3 and cam ring 1 are cyclically changed to effect the compression.
It is well known that, in this ordinary vane-type rotary compressor, the angle .alpha. formed between the direction of reciprocation of the vane 4 and the line normal to the cam ring 1 at the point of contact by the end of the vane 4 is preferably small in order to reduce the loss of energy due to friction during reciprocation of the vane. Namely, if this angle .alpha. is too large, a large friction takes place between the vane 4 and the walls of the vane groove 2 due to a moment imparted to the vane 4 because the direction of reactional force exerted on the vane 4 by the cam ring 1 does not coincide with the direction of the vane groove. To obviate this problem, it has been proposed to arrange the vane grooves 2 at a certain offset D from the center of the rotor 3 to diminish the angle .alpha..
As shown in FIG. 2, vane grooves 2 are formed to extend tangentially to an imaginary circle of 2D in diameter and concentric to the rotor 3, to thereby reduce the angle .alpha. during returning of the vane 4 to thereby diminish the friction between the vanes 4 and the vane grooves 2.
The offset arrangement of the vanes 4, however, imposes the following problem, although it is effective in reducing the loss of energy due to friction. Namely, as will be seen from FIGS. 3a, 3b and 3c, the cam ring 1 of the known vane-type rotary machine has an inner peripheral contour which is symmetrical with respect to the perpendicular bisector of the line interconnecting two adjacent points of contact between the cam ring 1 and the rotor 3 in adjacent lobes (n=1, 2, 3). Therefore, if the vane 4 offset D is zero, the movement of the vane in its forward stroke and the movement of the same in its backward stroke, which take place along the vane groove 2 as the rotor 3 rotates, are in perfect symmetry with each other with respect to the abovementioned perpendicular bisector. However, if the vane offset D is not zero, the movement of the vane 4 in its forward stroke and the movement of the same in its backward stroke are not in symmetry with each other. The movement of the vane 4 in relation to the rotation angle of the rotor will be explained more fully with reference to FIGS. 4a to 4d. Assuming a vane-type rotary machine having a 3-lobe type cam ring 1 provided with an inner peripheral contour expressed by r=40-5 cos 3.theta. (mm), FIG. 4a shows the amount r.sub.v (.theta.) of projection of the vane 4 from the rotor in relation to the rotation angle .theta. of the rotor. FIGS. 4b to 4d show, respectively, the differentiated values of the first, second and third degrees of the projection amount r.sub.v (.theta.). In these Figures, the full-line curves show the values as obtained when the offset D is zero, while the broken-line curves show the values as obtained when the offset D is 15 mm. Thus, r.sub.v shown in FIG. 4a shows the position of the vane 4, dr.sub.v /d.theta. shown in FIG. 4b represents the velocity of movement of the vane 4, d.sup.2 r.sub.v /d.theta..sup.2 shown in FIG. 4c represents the acceleration or inertia of the vane 4, and d.sup.3 r.sub.v /d.theta..sup.3 shown in FIG. 4d represents the rate of change of the inertia which is usually referred to as Jerk. As will be seen from these Figures, when the offset D is zero, all of the curves are ordinary sine curves due to the symmetric inner peripheral contour of the cam ring 1 expressed by r=40-5 cos .theta.. This means that the vane 4 can move smoothly and cyclically. In contrast, when there is an appreciable offset D, the curves are largely deviated from the sine curves. This means that the vane 4 moves in an irregular manner. Particularly, the rate of change of the inertia is seriously large. This irregular change in the inertia causes not only a phenomenon called chattering in which the vane 4 vibratorily comes into and out of contact with the cam ring but also various other problems such as breakage of oil film on the inner peripheral surface of the cam ring 1. Furthermore, the volume of the spaces behind respective vanes, which are all in communication with one another, is irregularly changed to promote the tendency of chattering to cause loss of heat.
It will be understood that the offset of the vane grooves 2, without being accompanied by a suitable change in the inner peripheral contour of the cam ring 1, makes the movement of the vanes 4 quite irregular to cause various problems such as increase of the friction loss and increased level of noise produced by the vanes. Consequently, the aforementioned advantage of the offset arrangement, i.e. the reduction of the friction loss through reduction in the reactional force produced at the point of contact between the end of the vane and the inner peripheral surface of the cam ring, is completely negated to make the vane offset arrangement meaningless. Thus, there is no substantial advantage in providing a large offset of the vane grooves. This problem is serious particularly when the number of lobes in the cam ring is increased.